Optokinetic nystagmus (OKN) or Optokinetic Reflex (OKR) is the rhythmic movement of the eyes when tracking a moving field. In particular, OKN can be induced by presenting a test subject with a drifting image of sinusoidally modulated gratings, where the eye experiences a slow or smooth phase in which the eye reflexively tracks the stimulus alternating with a saccadic or fast phase in which the eye rapidly re-fixates in the opposite direction and then begins to track again.
By adjusting the characteristics of the drifting image, contrast sensitivity thresholds and visual acuity of a test subject can be measured. These measurements are somewhat subjective because they require either responses from the test subjects themselves (e.g., when a visual cue is detected or not) and/or interpretation of the test subject's eye movements by the operator. The required inputs by the test subjects and/or operator can vary among tests, subjects, and operators, which pose challenges to physicians in deciphering, interpreting, and sharing test results for use in various purposes, such as diagnosis or academic research. Moreover, conventional tests are not particularly applicable to test subjects who are not able to understand or communicate detection of visual cues. In addition, conventional tests typically take a relatively long time to perform, e.g., 20-30 minutes or much longer depending on the test, which is an inconvenience for both the patient and the operator.
Further, conventional testing of visual function is generally done under “normal” lighting conditions (i.e., bright light). This is typically for convenience purposes because testing of visual function under different lighting conditions requires a readjustment period between one condition and the next before testing can take place. For instance, before a patient's visual function can be tested in a dark room, the patient must be placed in the dark room for about 15 minutes to allow their eyes to adjust to the dim or dark conditions. This readjustment is often called dark adapting or dark adaptation, and it is done to test the function of the rod photoreceptors, which are more sensitive to light than cone photoreceptors and the dominant detectors of light under dark conditions. They are saturated in bright light, so the less sensitive cone photoreceptors dominate in conventional testing conditions of bright light. Thus, conventional tests generally measure cone photoreceptors only. Along the same lines, once the subject has been in the dark for a while, the stimulus presented also has to be dimmer because a “normal” brightness will end up testing the less sensitive cones by supersaturating the rods. A less bright stimulus is too dim for the less sensitive cone photoreceptors to detect but perfect for the sensitive rod photoreceptors. Conventional tests are not applicable for darker testing conditions because they do not make brightness adjustments to account for testing of the rods.
Therefore, there is still a need for a method for testing visual capacity which reliably permits the objective testing of a test subject; which has application to human beings, animals such as mammals, and other forms of life; which achieves a degree of reliability significantly enhanced over that heretofore achieved in the art; which can be employed for the purpose of directly testing contrast sensitivity and/or visual acuity of the test subject as well as testing for a multiplicity of other physical conditions that may be evidenced, or otherwise evaluated, based on the contrast sensitivity and/or visual acuity of the test subject; which can be employed, more generally, in a multiplicity of environments wherein it is desirable, or of importance, to know the contrast sensitivity and/or visual acuity of the test subject without compromise or influence by subjective considerations; which is comparatively inexpensive to employ while being adaptable to virtually all operative environments such as lighting conditions; and which is otherwise entirely suited to achieving its operational objectives, and which can be completed in a short amount of time.
Traditional retinal function tests have difficulty testing for early detection of glaucoma, age related macular degeneration, and other similar eye diseases such as cataract and retinal dystrophy, for diagnosing malingering, and for vision testing in non-communicative patients, such as infants, toddlers, patients with neurological deficits or cognitive disorders, and animals.